This invention relates to thermal bypass valves for a heat exchanger circuit and a heat exchanger system using this type of valve.
Thermal bypass valves are well known in the art of heat exchangers. In particular such valves are commonly used with an oil cooler in order to help regulate the temperature of oil used in engines, transmissions, power steering systems and hydraulic systems. These known valves can provide a flow path by which the oil or heat exchange fluid passing to the valve from an oil source is returned without passing through a heat exchanger or oil cooler during a warm-up period.
An example of an oil cooler bypass valve is that taught in U.S. Pat. No. 6,935,569 which issued Aug. 30, 2005. This known cooler bypass valve has a responsive element that expands to urge a valve member against a valve seat and thereby causes transmission fluid to flow through an oil fluid cooler. A cast valve housing is utilized which is interposed between the cooler and the oil source. The valve actuating mechanism is designed to allow fluid to pass through the valve once the fluid has reached an elevated pressure level.
A possible deficiency with known oil cooler bypass valves is that, if they fail to operate as designed, this can result in substantial damage occurring to the machine or vehicle which requires the oil or heat exchange fluid to be within a desired temperature range in order to operate or in order to operate without undue wear. There is therefore a need to provide a thermal bypass valve which has a so called failsafe construction whereby, for example, in the event of the failure of a thermal actuator in the valve, the valve member will still be moved to a desired position (whether it be an open or closed position) that will prevent significant damage being caused to the machine or component that requires the oil or heat exchange fluid to be within a pre-determined temperature range.